1. Field of the Invention
The invention relates to a bitumen emulsion, a process of producing a bitumen emulsion and a process of producing a bituminous material for the construction or maintenance of pavements.
The invention more particularly relates to emulsions for surface coatings and emulsions for preparing cold mixes, as well as a process of producing such emulsions and a process of producing a bituminous material with such emulsions.
2. Discussion of Background
The emulsions referred to above are aqueous emulsions whose breaking is in part affected by the evaporation of the water. In the case of an aqueous emulsion of bitumen for a coating containing aggregates, the breaking of the emulsion causes the fixing of the aggregates on the surface of the pavement on which the coating has been spread, and the maintenance of cohesion between the aggregates. Various processes aimed at controlling the breaking have been tried, with a view to improving the quality of the coating. Examples of these processes include the simultaneous spreading on the pavement of an aqueous emulsion of bitumen and a breaking agent sprayed into the emulsion jet, so that the breaking of the emulsion occurs rapidly within the mass of the emulsion at the moment of spreading. Another solution consists of incorporating breaking agents in bitumen emulsion in the form of an emulsion or suspension in a solvent phase, or the use of breaking agents within an envelope created mechanically for example by the method known as rotative surfaces, for example by centrifugation.
In the case of an aqueous bitumen emulsion applied for the preparation of cold mixes, in general, and for the preparation of the wearing course of a pavement in particular, the breaking of the emulsion is also affected by the evaporation of the water, but differs from the breaking of the emulsions used for the first application in that the emulsion must remain stable for a long time and must in particular allow the complete coating of all the aggregate fractions, from the initial mixing step, during the transport of the mix and in the finishing leveller. In addition, the breaking of the emulsion must be able to be performed in such a way that the wearing course can be compacted and that the cohesion of the mix is homogeneous over the whole thickness of the coating. This requires both a long handling time and control of the breaking of the emulsion.
Document FR-A-2.618.350 describes a process allowing initiation the breaking of a bituminous emulsion by means of a breaking agent implemented in the form of microcapsules whose casing is a material which is chemically and/or physically attacked after a predetermined length of contact with the emulsion. This process allows the moment at which the breaking occurs to be delayed. However, once the breaking agent has been introduced and dispersed into the emulsion, the time at which the breaking occurs can no longer be changed, as it depends on the length of contact of the capsules with the emulsion. It follows that this known process does not allow the breaking of a bitumen emulsion to be controlled, but only to be delayed by some tens of minutes.
Moreover, the process cited above requires that the nature of the casing of the microcapsules is appropriate to that of the emulsion. Thus, an acid emulsion requires--in addition to a basic breaking agent--a casing sensitive to acids.